package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.Serializable;
import java.util.ArrayList;

/** Expert: Describes the score computation for document and query. */
public class Explanation implements java.io.Serializable {
    private float value; // the value of this node
    private String description; // what it represents
    private ArrayList<Explanation> details; // sub-explanations

    public Explanation() {
    }

    public Explanation(float value, String description) {
        this.value = value;
        this.description = description;
    }

    /**
     * Indicates whether or not this Explanation models a good match.
     *
     * <p>
     * By default, an Explanation represents a "match" if the value is positive.
     * </p>
     * @see #getValue
     */
    public boolean isMatch() {
        return (0.0f < getValue());
    }

    /** The value assigned to this explanation node. */
    public float getValue() {
        return value;
    }

    /** Sets the value assigned to this explanation node. */
    public void setValue(float value) {
        this.value = value;
    }

    /** A description of this explanation node. */
    public String getDescription() {
        return description;
    }

    /** Sets the description of this explanation node. */
    public void setDescription(String description) {
        this.description = description;
    }

    /**
     * A short one line summary which should contain all high level
     * information about this Explanation, without the "Details"
     */
    protected String getSummary() {
        return getValue() + " = " + getDescription();
    }

    /** The sub-nodes of this explanation node. */
    public Explanation[] getDetails() {
        if (details == null)
            return null;
        return details.toArray(new Explanation[0]);
    }

    /** Adds a sub-node to this explanation node. */
    public void addDetail(Explanation detail) {
        if (details == null)
            details = new ArrayList<Explanation>();
        details.add(detail);
    }

    /** Render an explanation as text. */
    @Override
    public String toString() {
        return toString(0);
    }

    protected String toString(int depth) {
        StringBuilder buffer = new StringBuilder();
        for (int i = 0; i < depth; i++) {
            buffer.append("  ");
        }
        buffer.append(getSummary());
        buffer.append("\n");

        Explanation[] details = getDetails();
        if (details != null) {
            for (int i = 0; i < details.length; i++) {
                buffer.append(details[i].toString(depth + 1));
            }
        }

        return buffer.toString();
    }

    /** Render an explanation as HTML. */
    public String toHtml() {
        StringBuilder buffer = new StringBuilder();
        buffer.append("<ul>\n");

        buffer.append("<li>");
        buffer.append(getSummary());
        buffer.append("<br />\n");

        Explanation[] details = getDetails();
        if (details != null) {
            for (int i = 0; i < details.length; i++) {
                buffer.append(details[i].toHtml());
            }
        }

        buffer.append("</li>\n");
        buffer.append("</ul>\n");

        return buffer.toString();
    }

    /**
     * Small Util class used to pass both an idf factor as well as an
     * explanation for that factor.
     * 
     * This class will likely be held on a {@link Weight}, so be aware 
     * before storing any large or un-serializable fields.
     *
     */
    public static abstract class IDFExplanation implements Serializable {
        /**
         * @return the idf factor
         */
        public abstract float getIdf();

        /**
         * This should be calculated lazily if possible.
         * 
         * @return the explanation for the idf factor.
         */
        public abstract String explain();
    }
}
